Casing Treatment and Inlet Swirl of Centrifugal Compressors

2012 ◽  
Author(s):  
Hua Chen ◽  
Vai-Man Lei
Keyword(s):  
Cost Effective ◽  
Centrifugal Compressors ◽  
Suction Surface ◽  
Blade Loading ◽  
Casing Treatment ◽  
Wall Boundary Layer ◽  
Flow Swirl ◽  
Flow Loss ◽  
Layer Region ◽  
Ported Shroud

Ported shroud is a cost effective casing treatment that can greatly improve stability of centrifugal compressors. It is widely used in turbochargers and other applications where compressors with wide flow range are required. This paper reviews the development of the ported shroud concept from its first conception in the 1980s to its current various configurations, explores the underline mechanisms that deliver the performance improvement. It is explained that by removing stagnant fluid from impeller inducer shroud end wall boundary-layer region and recirculating it to the impeller inlet, blade loading near the inducer shroud is increased with improved inlet suction. For transonic flow, ported shroud weakens the shock wave and reduces flow separation on the inducer suction surface. It is argued that the effectiveness of the ported shroud is a balance of blade loading and the flow loss inside the ported shroud cavity. The loss needs to be minimised if ported shroud is to be more effective. Blade loading may be increased by various methods such as using high inducer blade turning and using full bladed impellers. The blade loading can also be improved by removing flow swirl in ported shroud flow by vanes, or imposing negative swirl by vanes in ported shroud. Circumferential flow variation caused by volute housing can be taken into account by variable pitch vanes or by variable port position.

Casing Treatment and Inlet Swirl of Centrifugal Compressors

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Hua Chen ◽  
Vai-Man Lei
Keyword(s):  
Cost Effective ◽  
Centrifugal Compressors ◽  
Suction Surface ◽  
Blade Loading ◽  
Casing Treatment ◽  
Wall Boundary Layer ◽  
Flow Swirl ◽  
Flow Loss ◽  
Layer Region ◽  
Ported Shroud

Ported shroud is a cost-effective casing treatment that can greatly improve stability of centrifugal compressors. It is widely used in turbochargers and other applications where compressors with a wide flow range are required. This paper reviews the development of the ported shroud concept from its first conception in the 1980 s to its current various configurations and explores the underline mechanisms that deliver the performance improvement. It is explained that, by removing stagnant fluid from impeller inducer shroud end wall boundary-layer region and recirculating it to the impeller inlet, blade loading near the inducer shroud is increased with improved inlet suction. For transonic flow, the ported shroud weakens the shock wave and reduces flow separation on the inducer suction surface. It is argued that the effectiveness of ported shroud is a balance of blade loading and the flow loss inside the ported shroud cavity. The loss needs to be minimized if ported shroud is to be more effective. Blade loading may be increased by various methods, such as using high inducer blade turning and using full-bladed impellers. The blade loading can also be improved by removing flow swirl in ported shroud flow by vanes or imposing negative swirl by vanes in ported shroud. Circumferential flow variation caused by volute housing can be taken into account by variable pitch vanes or by variable port position.

Casing Treatment of Centrifugal Compressors

2015 ◽  
Author(s):  
Jisha Noushad ◽  
Anand Babu Dhamarla ◽  
Pavan Kumar
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Pressure Fluctuations ◽  
Centrifugal Compressors ◽  
Flow Rates ◽  
Casing Treatment ◽  
Operating Range ◽  
Mass Flow Rates ◽  
Ported Shroud

The operating range of any compressor is controlled by Surge and Choke. Surge occurs at lower mass flow rates with large pressure fluctuations and flow reversals, while choke occurs at higher mass flow rates when the flow rate reaches the limit which compressor can discharge. Ported shroud is a cost effective casing treatment that can greatly improve operating range of centrifugal compressors. By removing the stagnant and reverse flow from shroud wall boundary-layer region and recirculating it to impeller inlet, it has been demonstrated that larger range of operability can be achieved without much loss on compressor efficiency. This paper demonstrates the improvement of a centrifugal compressor operational range with ported shroud configuration. A series of CFD simulations were carried out with open source centrifugal compressor geometry (NASA HPCC 4:1) to create performance characteristics/speed-lines. The CFD methodology and practices were validated by comparing the results with the experimental data. Performance evaluation of ported shroud configuration is done with respect to solid shroud. Ported shroud compressor is proven to give higher choke mass flow and also a better surge margin compared to the Solid shroud model. The phenomena of in-flowing and out-flowing port have also been demonstrated. Emphasis was given to understand how ported shroud helps to achieve a better performance. A design optimization study has also been carried out in order to establish the optimum ported shroud configuration. Design parameter such as port location has been selected and the effect of this parameter on the performance of the compressor is studied using CFD. Optimum port geometry was proposed.

Numerically Derived Design Guidelines of Self Recirculation Casing Treatment for Industrial Centrifugal Compressors

2016 ◽  
Author(s):  
Sewoong Jung ◽  
Robert Pelton
Keyword(s):  
Fluid Dynamic ◽  
Cost Effective ◽  
High Volume ◽  
Design Guidelines ◽  
Slot Width ◽  
Optimized Design ◽  
Centrifugal Compressors ◽  
Casing Treatment ◽  
High Volume Production ◽  
Derived Design

Casing treatments are a well-known method to extend operating range of centrifugal compressors. A common casing treatment configuration consists of a passage that allows flow from the impeller shroud to be bleed back to the inlet of the stage. This type of casing treatment is used frequently in some applications, including automotive turbochargers, but is rarely used in industrial compressors. An effective casing treatment must be developed specifically to match a given stage. For high volume production products this is practical. For the wide variety of industrial compressor designs, which are produced in low volumes, it is not often cost effective to design a casing treatment to match each application. To help reduce the design effort associated with developing a new casing treatment design, a simple set of design guidelines were developed. These guidelines are based on the results of a computational fluid dynamic (CFD) study of several different class impellers. These guidelines can be used to correctly locate and size the key geometric features of a self-recirculating casing treatment, including slot width, position and cavity vane profile. The study found that the bleed slot position and width were the primary factors controlling performance of the casing treatment. In general, when the slot width is wider and the bleed position is moved further downstream, the range increases but the efficiency falls. The optimal slot width is found to be when the slot area is 23% of the area of inducer eye and positioning the slot near the impeller throat gives a good balance of increased range with minimal efficiency loss. A well designed casing treatment is expected to result in approximately a 25% increase in range while keeping the drop in efficiency less than 0.4 point for the cases considered in this study. In addition, the rise to surge increased more than 60% and turndown almost doubled value with the optimized design.

Experimental investigation of an active control casing treatment of centrifugal compressors

2017 ◽  
Vol 83 ◽  
pp. 107-117 ◽  
Author(s):  
Qichao Yang ◽  
Liansheng Li ◽  
Yuanyang Zhao ◽  
Jun Xiao ◽  
Yue Shu ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Active Control ◽  
Centrifugal Compressors ◽  
Casing Treatment

scholarly journals Reduction of Unsteady Blade Loading by Beneficial Use of Vortical and Potential Disturbances in an Axial Compressor With Rotor Clocking

1998 ◽  
Vol 120 (4) ◽  
pp. 705-713 ◽  
Author(s):  
S. T. Hsu ◽  
A. M. Wo
Keyword(s):  
Large Scale ◽  
Axial Compressor ◽  
Leading Edge ◽  
Forced Response ◽  
Suction Surface ◽  
Blade Loading ◽  
Beneficial Use ◽  
Unsteady Loading ◽  
Vortical Disturbance ◽  
First Time

This paper demonstrates reduction of stator unsteady loading due to forced response in a large-scale, low-speed, rotor/stator/rotor axial compressor rig by clocking the downstream rotor. Data from the rotor/stator configuration showed that the stator response due to the upstream vortical disturbance reaches a maximum when the wake impinges against the suction surface immediately downstream of the leading edge. Results from the stator/rotor configuration revealed that the stator response due to the downstream potential disturbance reaches a minimum with a slight time delay after the rotor sweeps pass the stator trailing edge. For the rotor/stator/rotor configuration, with Gap1 = 10 percent chord and Gap2 = 30 percent chord, results showed a 60 percent reduction in the stator force amplitude by clocking the downstream rotor so that the time occurrence of the maximum force due to the upstream vortical disturbance coincides with that of the minimum force due to the downstream potential disturbance. This is the first time, the authors believe, that beneficial use of flow unsteadiness is definitively demonstrated to reduce the blade unsteady loading.

A Meanline Model for Impeller Flow Recirculation

2008 ◽  
Author(s):  
Xuwen Qiu ◽  
David Japikse ◽  
Mark Anderson
Keyword(s):  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Low Flow ◽  
Suction Surface ◽  
Blade Loading ◽  
Flow Recirculation ◽  
Impeller Outlet ◽  
Active Flow ◽  
Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

scholarly journals Control of the Unsteady Flow in a Stator Blade Row Interacting With Upstream Moving Wakes

1993 ◽  
Author(s):  
T. Valkov ◽  
C. S. Tan
Keyword(s):  
Unsteady Flow ◽  
Pressure Fluctuations ◽  
Spectral Element ◽  
Navier Stokes ◽  
Suction Surface ◽  
Model Calculations ◽  
Blade Loading ◽  
Pressure Surface ◽  
Blade Row ◽  
Stator Blade

A computational approach, based on a spectral-element Navier-Stokes solver, has been applied to the study of the unsteady flow arising from wake-stator interaction. Direct, as well as turbulence-model calculations, provide insight into the mechanics of the unsteady flow and demonstrate the potential for controlling its effects. The results show that the interaction between the wakes and the stator blades produces a characteristic pattern of vortical disturbances, which have been correlated to the pressure fluctuations. Within the stator passage, the wakes migrate towards the pressure surface where they evolve into counter-rotating vortices. These vortices are the dominant source of disturbances over the pressure surface of the stator blade. Over the suction surface of the stator blade, the disturbances are due to the distortion and detachment of boundary layer fluid. They can be reduced by tailoring the blade loading or by applying non-uniform suction.

Ported Shroud Flow Processes and Their Effect on Turbocharger Compressor Operation

2017 ◽  
Author(s):  
Sidharath Sharma ◽  
Martyn L. Jupp ◽  
Ambrose K. Nickson ◽  
John M. Allport
Keyword(s):  
Entropy Generation ◽  
Primary Source ◽  
Navier Stokes ◽  
Stable Operation ◽  
Casing Treatment ◽  
Flow Processes ◽  
Compressor Inlet ◽  
Flow Mechanisms ◽  
Sst Turbulence Model ◽  
Ported Shroud

The ported shroud (PS) self-recirculating casing treatment is widely used to delay the onset of the surge by enhancing the aerodynamic stability of the turbocharger compressor. The increase in the stable operation region of the turbocharger compressor is achieved by recirculating the low momentum fluid that blocks the blade passage to the compressor inlet through a ported shroud cavity. While the ported shroud design delays surge, it comes with a small penalty in efficiency. This work presents an investigation of the flow processes associated with a ported shroud compressor and quantifies the effect of these flow mechanisms on the compressor operation. The full compressor stage is numerically modelled using a Reynolds Averaged Navier-Stokes (RANS) approach employing the shear stress transport (SST) turbulence model for steady state simulations at the design and near surge conditions. The wheel rotation is modelled using a multiple reference frame (MRF) approach. The results show that the flow exits the PS cavity at the near surge condition in the form of three jet-like structures of varying velocity amplitudes. Net entropy generation in the compressor model is used to assess the influence of the ported shroud design on the compressor losses, and the results indicate a small Inlet-PS mixing region is the primary source of entropy generation in the near surge conditions. The analysis also explores the trends of entropy generation at the design and the near surge condition across the different speed lines. The results show that the primary source of entropy generation is the impeller region for the design condition and the inlet-PS cavity region for the near surge condition.

Performance Prediction of a Novel Design for Turbine Vane Film Cooling With Low Aerodynamic Loss and High Effectiveness

2004 ◽  
Author(s):  
William D. York ◽  
James H. Leylek
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Density Ratio ◽  
Leading Edge ◽  
Cost Effective ◽  
Design Environment ◽  
Suction Surface ◽  
Reference Case ◽  
Aerodynamic Loss ◽  
Turbine Vane

A new film-cooling scheme for the suction surface of a gas turbine vane in a transonic cascade is studied numerically. The concept of the present design is to inject a substantial amount of coolant at a very small angle, approaching a “wall-jet,” through a single row of relatively few, large holes near the vane leading edge. The near-match of the coolant stream and mainstream momentums, coupled with the low coolant trajectory, theoretically results in low aerodynamic losses due to mixing. A minimal effect of the film cooling on the vane loading is also important to realize, as well as good coolant coverage and high adiabatic effectiveness. A systematic computational methodology, developed in the Advanced Computational Research Laboratory (ACRL) and tested numerous times on film-cooling applications, is applied in the present work. For validation purposes, predictions from two previous turbine airfoil film-cooling studies, both employing this same numerical method, are presented and compared to experimental data. Simulations of the new film-cooling configuration are performed for two blowing ratios, M=0.90 and M=1.04, and the density ratio of the coolant to the mainstream flow is unity in both cases. A solid vane with no film cooling is also studied as a reference case in the evaluation of losses. The unstructured numerical mesh contains about 5.5 million finite-volumes, after solution-based adaption. Grid resolution is such that the full boundary layer and all passage shocks are resolved. The Renormalization Group (RNG) k-ε turbulence model is used to close the Reynolds-averaged Navier-Stokes equations. Predictions indicate that the new film-cooling scheme meets design intent and has negligible impact on the total pressure losses through the vane cascade. Additionally, excellent coolant coverage is observed all the way to the trailing edge, resulting in high far-field effectiveness. Keeping the design environment in mind, this work represents the power of validated computational methods to provide a rapid and reasonably cost-effective analysis of innovative turbine airfoil cooling.

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